1. CCl 4 Sorption and Degradation on Fe-oxide surfaces Jeff Fitts, Kwang Rim 1, George Flynn 1, Kaveh Adib 2, Nick Camillone III 2, Richard Osgood 2, Peter Schlosser 3, Steve Joyce 4 Environmental Molecular Sciences Institute Columbia University, New York, NY 2 Electrical Engineering 1 Chemistry 3 Environmental Engineering 4 EMSL @ PNNL

2. Organochlorine compounds: PCBs, DDT, CCl 4... Extensive point source contamination and elevated global background levels. Compounds readily react on certain metal oxide surfaces. CCl 4 : oxides of V, Cr, Ti and Fe C-Cl CO+MeCl=MeO surf + High levels observed in human tissue, blood and breast milk. Compounds are hormonally active, toxic and carcinogenic.

3. Not all phases of Fe-(hydr)oxides react with CCl 4 Fe oxide phase Fe oxidation state CoordinationAqueous Reactivity Non-aqueous (UHV) FeOOH (goethite)3+OctahedralNR? w/ adsorbed Fe 2+ 3+ReactiveOctahedral? Fe 2 O 3 (hematite)3+OctahedralNR ? Fe 3 O 4 (magnetite)2+,3+Oct. & Tet.Reactive? Fe 1-x O (wustite) 2+ Oct. & Tet.?? Fe metal (ZVI)0,2+,3+ - Reactive

4. Project goals Determine whether CCl 4 reacts at hematite, magnetite and wustite surfaces in UHV. Identify unique characteristics of Fe-oxides surfaces responsible for observed reactivity.

5. Experimental Approach

6. Heat Surface preparation in ultrahigh vacuum (UHV) in pO 2 = 10 -6 -10 -5 T Heat Chamber with base pressure = 3x10 -10 T Ar + ion sputtering 1-2kV, 3-10  A Annealing 950-1100K in UHV Characterize surface phase with LEED Ion gun LN 2 Heat

8. Surface preparation conditions control surface Fe-oxide phase

9. Heat Temperature Programmed Desorption (TPD) experiments LN 2 Heat QMS CCl 4 multi-layer desorption CCl 4 monolayer desorption Recombinative desorption of CCl 4 and C 2 Cl 4 FeCl 2 Dosing tube OCCl 2 (phosgene) desorption

10. Proposed reactions of CCl 4 on Fe 3 O 4 (III) surface Recombinative Desorption C Cl O Fe 3 O 4 (III) Cl Fe Fe 3 O 4 (III) 2 X 2Cl + CCl 2 CCl 4 2CCl 2 C 2 Cl 4 SurfaceAbstraction FeCl 2 OCCl 2

11. How much of the surface reacts with CCl 4 ? Amount of CCl 4 desorbed (a.u.) No CCl 4 desorbs after doses of < 1 ML 0.3 L dose contains enough CCl 4 to cover entire surface (1 ML  20%) CCl 4 does not only react at minority site (e.g., defects). CCl 4 must react at site(s) that cover the entire surface.

12. Initial dose Where does the reaction occur? Between doses: anneal to 450 K No FeCl 2 desorption OCCl 2 production Fe-Cl surface species inhibit CCl 4 degradation reactions

13. What did we learn from the TPD studies? What do we want to know about these reactions? What type of surface site reacts with CCl 4 ? How do Fe-Cl species inhibit CCl 4 degradation? Fe-Cl surface species inhibit further reaction This reaction likely occurs at regular surface sites CCl 4 readily reacts with the Fe 3 O 4 (111) surface to predominantly form OCCl 2